Lubricant oil composition and internal-combustion-engine friction reduction method

ABSTRACT

A lubricating oil composition which exhibits an excellent friction-reducing effect and excellent fuel consumption reducing properties is provided. 
     The lubricating oil composition includes a lubricating base oil (A), a molybdenum compound (B), and an ashless friction modifier (C), wherein the lubricating oil composition includes a binuclear organic molybdenum compound represented by the following general formula (I) as the molybdenum compound (B), with the content of the binuclear organic molybdenum compound as converted into molybdenum atoms being 0.030 mass % or more and 0.140 mass % or less based on the total amount of the lubricating oil composition; and an ester-based ashless friction modifier (C1) and/or an amine-based ashless friction modifier (C2) as the ashless friction modifier (C), with the total content of the ester-based ashless friction modifier (C1) and the amine-based ashless friction modifier (C2) being more than 0.1 mass % and 1.8 mass % or less based on the total amount of the lubricating oil composition: 
     
       
         
         
             
             
         
       
         
         
           
             in the general formula (I), R 1  to R 4  each represents a hydrocarbon group having 4 to 22 carbon atoms, R 1  to R 4  may be the same as or different from each other, and X 1  to X 4  each represents a sulfur atom or an oxygen atom.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition and amethod for reducing friction of an internal combustion engine.

BACKGROUND ART

In recent years, following the strengthening of environmentalregulations, high fuel consumption reducing properties have beenrequired for engine oils. For this reason, efforts have been maderegarding blending a molybdenum compound such as molybdenumdithiocarbamate (MoDTC) into a lubricating oil composition, therebyreducing a metal-to-metal friction coefficient.

The molybdenum compound such as MoDTC exhibits a friction-reducingeffect in a relatively high temperature region of 80° C. or higher.Examples of the lubricating oil composition having a molybdenum compoundblended therein include those disclosed in PTL 1.

Meanwhile, ashless friction modifiers such as an ester-based frictionmodifier and an amine-based friction modifier are also used so as toreduce friction (for example, PTL 2).

These ashless friction modifiers have excellent friction-reducingeffects in a relatively low temperature region of lower than 80° C.

Taking into consideration the friction-reducing characteristics of amolybdenum compound in a high-temperature region and thefriction-reducing characteristics of an ashless friction modifier in alow-temperature region, it can be expected that a friction-reducingeffect is exhibited in a wide temperature region by using a molybdenumcompound in combination with an ashless friction modifier.

CITATION LIST Patent Literature

PTL 1: JP 2015-010177 A

PTL 2: WO 2011/062282 A

SUMMARY OF INVENTION Technical Problem

However, in a case of using a molybdenum compound in combination with anashless friction modifier, there was involved such a problem that theashless friction modifier inhibits a friction-reducing effect of themolybdenum compound, and consequently, impairs fuel consumption reducingproperties.

It is an object of the present invention to provide a lubricating oilcomposition which exhibits an excellent friction-reducing effect andexcellent fuel consumption reducing properties.

Solution to Problem

In order to solve the aforementioned problem, an embodiment of thepresent invention provides a lubricating oil composition including alubricating base oil (A), a molybdenum compound (B), and an ashlessfriction modifier (C),

wherein the lubricating oil composition includes a binuclear organicmolybdenum compound represented by the following general formula (I) asthe molybdenum compound (B), with the content of the binuclear organicmolybdenum compound as converted into molybdenum atoms being 0.030 mass% or more and 0.140 mass % or less based on the total amount of thelubricating oil composition; and

an ester-based ashless friction modifier (C1) and/or an amine-basedashless friction modifier (C2) as the ashless friction modifier (C),with the total content of the ester-based ashless friction modifier (C1)and the amine-based ashless friction modifier (C2) being more than 0.1mass % and 1.8 mass % or less based on the total amount of thelubricating oil composition:

in the general formula (I), R¹ to R⁴ each represents a hydrocarbon grouphaving 4 to 22 carbon atoms, R¹ to R⁴ may be the same as or differentfrom each other, and X¹ to X⁴ each represents a sulfur atom or an oxygenatom.

Advantageous Effect of Invention

Since the lubricating oil composition of the present invention makes itpossible to use the molybdenum compound in combination with an ashlessfriction modifier without inhibiting the friction-reducing effect of amolybdenum compound, the lubricating oil composition exhibits anexcellent friction-reducing effect and can enhance fuel consumptionreducing properties.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described.

[Lubricating Oil Composition]

The lubricating oil composition of the present embodiment is alubricating oil composition including a lubricating base oil (A), amolybdenum compound (B), and an ashless friction modifier (C),

wherein the lubricating oil composition includes a binuclear organicmolybdenum compound represented by the following general formula (I) asthe molybdenum compound (B), with the content of the binuclear organicmolybdenum compound as converted into molybdenum atoms being 0.030 mass% or more and 0.140 mass % or less based on the total amount of thelubricating oil composition; and

an ester-based ashless friction modifier (C1) and/or an amine-basedashless friction modifier (C2) as the ashless friction modifier (C),with the total content of the ester-based ashless friction modifier (C1)and the amine-based ashless friction modifier (C2) being more than 0.1mass % and 1.8 mass % or less based on the total amount of thelubricating oil composition:

in the general formula (I), R¹ to R⁴ each represents a hydrocarbon grouphaving 4 to 22 carbon atoms, R¹ to R⁴ may be the same as or differentfrom each other, and X¹ to X⁴ each represents a sulfur atom or an oxygenatom.

<(A) Lubricating Base Oil>

The lubricating oil composition of the present embodiment includes alubricating base oil (A). Examples of the lubricating base oil as thecomponent (A) include a mineral oil and/or a synthetic oil.

Examples of the mineral oil include a paraffin-based mineral oil, anintermediate-based mineral oil, and a naphthene-based mineral oil,obtained by a usual refining method such as solvent refining andhydrogenation refining; and wax-isomerized oils produced by isomerizinga wax such as a wax (a gas-to-liquid wax) produced by a Fischer-Tropschprocess or the like, and a mineral oil-based wax.

Examples of the synthetic oil include a hydrocarbon-based synthetic oiland an ether-based synthetic oil. Examples of the hydrocarbon-basedsynthetic oil include an α-olefin oligomer such as polybutene,polyisobutylene, a 1-octene oligomer, a 1-decene oligomer, and anethylene-propylene copolymer, or a hydride thereof; an alkylbenzene; andan alkylnaphthalene. Examples of the ether-based synthetic oil includepolyoxyalkylene glycol and polyphenyl ether.

Although the lubricating base oil (A) may be of a single system usingone of the aforementioned mineral oils and synthetic oils, it may alsobe of a mixed system, for example, a mixture of two or more mineraloils, a mixture of two or more synthetic oils, or a mixture of each oneor each two or more of mineral oils and synthetic oils.

In particular, it is preferable to use one or more selected from mineraloils or synthetic oils classified into Group 3 and Group 4 in the baseoil classification of the American Petroleum Institute as thelubricating base oil (A).

The content of the lubricating base oil (A) is preferably 60 mass % ormore, more preferably 65 mass % or more and 95 mass % or less, and stillmore preferably 70 mass % or more and 85 mass % or less, based on thetotal amount of the lubricating oil composition.

<Molybdenum Compound (B)>

The lubricating oil composition of the present embodiment includes amolybdenum compound (B). Further, the lubricating oil composition of thepresent embodiment includes a binuclear organic molybdenum compoundrepresented by the following general formula (I) as the molybdenumcompound of the component (B), and the content of the binuclear organicmolybdenum compound as converted into molybdenum atoms is 0.030 mass %or more and 0.140 mass % or less based on the total amount of thelubricating oil composition.

In the general formula (I), R¹ to R⁴ each represents a hydrocarbon grouphaving 4 to 22 carbon atoms, and R¹ to R⁴ may be the same as ordifferent from each other. When the number of carbon atoms is 3 or less,the oil solubility becomes poor, whereas when the number of carbon atomsis 23 or more, the melting point becomes high, the handling becomesdeteriorated, and the friction-reducing ability becomes low. From theviewpoints, the number of carbon atoms is preferably 4 to 18, and morepreferably 8 to 13.

Examples of the hydrocarbon group of R¹ to R⁴ include an alkyl group, analkenyl group, an alkylaryl group, a cycloalkyl group, and acycloalkenyl group. A branched or linear alkyl group or alkenyl group ispreferable, and a branched or linear alkyl group is more preferable.Examples of the branched or linear alkyl group include an n-octyl group,a 2-ethylhexyl group, an isononyl group, an n-decyl group, an isodecylgroup, a dodecyl group, a tridecyl group, and an isotridecyl group.

Furthermore, from the viewpoints of solubility in the base oil, storagestability, and friction-reducing ability, in the binuclear organicmolybdenum compound represented by the general formula (I), it ispreferable that R¹ and R² are the same alkyl group, R³ and R⁴ are thesame alkyl group, and the alkyl groups of R¹ and R² and the alkyl groupsof R³ and R⁴ are different from each other.

Moreover, in the general formula (I), X¹ to X⁴ each represents a sulfuratom or an oxygen atom, and X¹ to X⁴ may be the same as or differentfrom each other. The ratio of the sulfur atoms to the oxygen atoms ispreferably 1/3 to 3/1, and more preferably 1.5/2.5 to 3/1 as convertedinto sulfur atoms/oxygen atoms. When the ratio falls within the range,good performance is obtained in view of corrosion resistance andsolubility in a lubricating base oil. In addition, all of X¹ to X⁴ mayalso be a sulfur atom or an oxygen atom.

In the lubricating oil composition of the present embodiment, thecontent of the binuclear organic molybdenum compound as converted intomolybdenum atoms needs to be 0.030 mass % or more and 0.140 mass % orless based on the total amount of the lubricating oil composition.

In a case where the content of the binuclear organic molybdenum compoundas converted into molybdenum atoms is less than 0.030 mass %, thefriction-reducing effect in a high-temperature region cannot beenhanced, and thus, fuel consumption reducing properties cannot besatisfied. Further, in a case where the content of the binuclear organicmolybdenum compound as converted into molybdenum atoms is more than0.140 mass %, cleanness is deteriorated.

The content of the binuclear organic molybdenum compound as convertedinto molybdenum atoms is preferably 0.050 to 0.120 mass %, and morepreferably 0.060 to 0.100 mass %, based on the total amount of thelubricating oil composition.

In addition, the lubricating oil composition of the present embodimentmay further contain a mononuclear organic molybdenum compound and/or atrinuclear organic molybdenum compound as the molybdenum compound.

<Ashless Friction Modifier (C)>

The lubricating oil composition of the present embodiment includes anashless friction modifier (C). Further, the lubricating oil compositionof the present embodiment includes an ester-based ashless frictionmodifier (C1) and/or an amine-based ashless friction modifier (C2) asthe ashless friction modifier of the component (C), and the totalcontent of the ester-based ashless friction modifier (C1) and theamine-based ashless friction modifier (C2) is more than 0.1 mass % and1.8 mass % or less based on the total amount of the lubricating oilcomposition.

Moreover, in the present embodiment, in a case where the ester-basedashless friction modifier (C1) is not included and only the amine-basedashless friction modifier (C2) is included, the content of theamine-based ashless friction modifier (C2) falls within the range.Further, in the present embodiment, in a case where the amine-basedashless friction modifier (C2) is not included and only the ester-basedashless friction modifier (C1) is included, the content of theester-based ashless friction modifier (C1) falls within the range. Inaddition, in various suitable embodiments which will be described later,in a case where only any one of the ester-based ashless frictionmodifier (C1) and the amine-based ashless friction modifier (C2) isincluded, the one ashless friction modifier satisfies various suitableembodiments.

In a case where the total content of the ester-based ashless frictionmodifier (C1) and the amine-based ashless friction modifier (C2) is 0.1mass % or less based on the total amount of the lubricating oilcomposition, it is not possible to impart a friction-reducing effectbased on the component (C1) and/or the component (C2). Further, in acase where the total content of the ester-based ashless frictionmodifier (C1) and the amine-based ashless friction modifier (C2) is morethan 1.8 mass % based on the total amount of the lubricating oilcomposition, a friction-reducing effect based on the molybdenum compound(B) is inhibited, and in turn, the friction coefficient increases.

Meanwhile, by allowing the lubricating oil composition of the presentembodiment to use the ester-based ashless friction modifier (C1) and/orthe amine-based ashless friction modifier (C2) as the ashless frictionmodifier of the component (C), and allowing the total content of thesecomponents to fall within the range, the lubricating oil composition canenhance the friction-reducing effect, and thus enhance the fuelconsumption reducing properties.

The total content of the ester-based ashless friction modifier (C1) andthe amine-based ashless friction modifier (C2) is preferably 0.2 mass %or more and 1.7 mass % or less, and more preferably 0.4 mass % or moreand 1.6 mass % or less, based on the total amount of the lubricating oilcomposition.

Ester-Based Ashless Friction Modifier (C1)

Various ester compounds can be used as the ester-based ashless frictionmodifier of the component (C1), in which an ester compound having one ormore hydroxyl groups in a molecule thereof is preferable, and an estercompound having two or more hydroxyl groups in a molecule thereof ismore preferable.

In addition, the ester compound having one or more hydroxyl groups in amolecule thereof preferably has 2 to 24 carbon atoms, more preferablyhas 10 to 24 carbon atoms, and still more preferably has 16 to 22 carbonatoms.

Examples of the ester compound having one or more hydroxyl groups in amolecule thereof include an ester compound having one hydroxyl group ina molecule thereof as in the following general formula (II) and acompound having two hydroxyl groups in a molecule thereof as in thefollowing general formula (III). Among these, a compound represented bythe general formula (III) is suitable.

In the general formulae (II) and (III), R⁵ and R¹⁰ are each ahydrocarbon group having 1 to 32 carbon atoms.

The number of carbon atoms of the hydrocarbon group of R⁵ and R¹⁰ ispreferably 8 to 32, more preferably 12 to 24, and still more preferably16 to 20.

Examples of the hydrocarbon group of R⁵ and R¹⁰ include an alkyl group,an alkenyl group, an alkylaryl group, a cycloalkyl group, and acycloalkenyl group. Among these, an alkyl group or an alkenyl group ispreferable, with an alkenyl group being more preferable.

Examples of the alkyl group in R⁵ and R¹⁰ include a methyl group, anethyl group, a propyl group, a butyl group, a pentyl group, a hexylgroup, a heptyl group, an octyl group, a nonyl group, a decyl group, anundecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, apentadecyl group, a hexadecyl group, a heptadecyl group, an octadecylgroup, a nonadecyl group, an eicosyl group, a heneicosyl group, adocosyl group, a tricosyl group, and a tetracosyl group. These may belinear, branched, or cyclic.

Furthermore, examples of the alkenyl group in R⁵ and R¹⁰ include a vinylgroup, a propenyl group, a butenyl group, a pentenyl group, a hexenylgroup, a heptenyl group, an octenyl group, a nonenyl group, a decenylgroup, an undecenyl group, a dodecenyl group, a tridecenyl group, atetradecenyl group, a pentadecenyl group, a hexadecenyl group, aheptadecenyl group, an octadecenyl group, a nonadecenyl group, aneicosenyl group, a heneicosenyl group, a docosenyl group, a tricosenylgroup, and a tetracosenyl group. These may be linear, branched, orcyclic, and the position of the double bond is arbitrary.

R⁶ to R⁹ and R¹¹ to R¹⁵ are each a hydrogen atom or a hydrocarbon grouphaving 1 to 18 carbon atoms, and they may be the same as or differentfrom each other.

In the general formula (II), it is preferable that all of R⁶ to R⁹ are ahydrogen atom, or all of R⁶ to R⁸ are a hydrogen atom, and R⁹ is ahydrocarbon group. Further, in the general formula (III), it ispreferable that all of R¹¹ to R¹⁵ are a hydrogen atom.

In a case where the compound represented by the general formula (II) isused as the ester-based ashless friction modifier (C1), a single kind ofthe compound in which all of R⁵'s to R⁹'s are all the same may be used,or a mixture of two or more kinds of the compounds in which some of R⁵'sto R⁹'s are different (for example, those in which the number of carbonatoms or the presence or absence of a double bond of R⁵'s is different)may be used. Similarly, in a case where the compound represented by thegeneral formula (III) is used as the ester-based ashless frictionmodifier (C1), a single kind of the compound in which all of R¹⁰'s toR¹⁵'s are all the same may be used, or a mixture of two or more kinds ofthe compounds in which R¹⁰'s to R¹⁵'s are different (for example, thosein which the number of carbon atoms or the presence or absence of adouble bond of R¹⁰'s is different, or R¹¹'s to R¹⁵'s are different) maybe used.

In a case where R⁶ to R⁹ and R¹¹ to R¹⁵ are a hydrocarbon group, thehydrocarbon group may be either saturated or unsaturated, may be eitheraliphatic or aromatic, and may be linear, branched, or cyclic.

Furthermore, in the general formula (II), “a” represents an integer of 1to 20, and is preferably 1 to 12, and more preferably 1 to 10.

The compound represented by the general formula (II) is, for example, acompound obtained through a reaction of a fatty acid and an alkyleneoxide.

Here, examples of the fatty acid for obtaining the compound representedby the general formula (II) include lauric acid, myristic acid, palmiticacid, oleic acid, tallow acid, and coconut fatty acid. Examples of thealkylene oxide include alkylene oxides having 2 to 12 carbon atoms, andspecific examples thereof include ethylene oxide, propylene oxide,butylene oxide, hexylene oxide, octylene oxide, decylene oxide, anddodecylene oxide.

Examples of the compound of the general formula (II) includepolyoxyethylene monolaurate, polyoxyethylene monostearate, andpolyoxyethylene monooleate.

Examples of the compound represented by the general formula (III)include glycerin fatty acid monoesters such as glycerin monolaurate,glycerin monostearate, glycerin monomyristate, and glycerin monooleate.Among these, glycerin monooleate is suitable.

Amine-Based Ashless Friction Modifier (C2)

As the amine-based ashless friction modifier (C2), an aliphaticamine-based compound is suitable, and an aliphatic amine-based compoundhaving one or more hydroxyl groups in a molecule thereof is moresuitable. Further, the amine-based ashless friction modifier (C2) may beany one of primary, secondary, and tertiary amines, with a tertiaryamine being suitable.

Examples of the amine-based ashless friction modifier (C2) which is atertiary amine, as the aliphatic amine-based compound having one or morehydroxyl groups in a molecule thereof, include compounds represented bythe following general formulae (IV) and (V), with a compound representedby the general formula (IV) being suitable.

In the general formulae (IV) and (V), R¹⁶, R²⁵, and R²⁶ are each ahydrocarbon group having 1 to 32 carbon atoms, and R²⁵ and R²⁶ may bethe same as or different from each other.

The number of carbon atoms of the hydrocarbon group of R¹⁶, R²⁵, and R²⁶is preferably 8 to 32, more preferably 10 to 24, and still morepreferably 12 to 20.

Examples of the hydrocarbon group of R¹⁶, R²⁵, and R²⁶ include an alkylgroup, an alkenyl group, an alkylaryl group, a cycloalkyl group, and acycloalkenyl group. Among these, an alkyl group or an alkenyl group ispreferable.

Examples of the alkyl group of R¹⁶, R²⁵, and R²⁶ include a methyl group,an ethyl group, a propyl group, a butyl group, a pentyl group, a hexylgroup, a heptyl group, an octyl group, a nonyl group, a decyl group, anundecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, apentadecyl group, a hexadecyl group, a heptadecyl group, an octadecylgroup, a nonadecyl group, an eicosyl group, a heneicosyl group, adocosyl group, a tricosyl group, and a tetracosyl group. These may belinear, branched, or cyclic.

Furthermore, examples of the alkenyl group represented by R¹⁶, R²⁵, andR²⁶ include a vinyl group, a propenyl group, a butenyl group, a pentenylgroup, a hexenyl group, a heptenyl group, an octenyl group, a nonenylgroup, a decenyl group, an undecenyl group, a dodecenyl group, atridecenyl group, a tetradecenyl group, a pentadecenyl group, ahexadecenyl group, a heptadecenyl group, an octadecenyl group, anonadecenyl group, an eicosenyl group, a heneicosenyl group, a docosenylgroup, a tricosenyl group, and a tetracosenyl group. These may belinear, branched, or cyclic, and the position of the double bond isarbitrary.

R¹⁷ to R²⁴ and R²⁷ to R³⁰ are each a hydrogen atom, a hydrocarbon grouphaving 1 to 18 carbon atoms, or an oxygen-containing hydrocarbon groupthat contains an ether bond or an ester bond. These may be the same asor different from each other, and each is preferably a hydrogen atom orthe hydrocarbon group.

The hydrocarbon group of R¹⁷ to R²⁴ and R²⁷ to R³⁰ may be saturated orunsaturated, aliphatic or aromatic, and linear, branched or cyclic, andexamples of the hydrocarbon group include aliphatic hydrocarbon groupssuch as an alkyl group and an alkenyl group, and aromatic hydrocarbongroups. More specific examples thereof include aliphatic hydrocarbongroups such as a methyl group, an ethyl group, a propyl group, a butylgroup, a butenyl group, a hexyl group, a hexenyl group, an octyl group,an octenyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, anundecyl group, a decenyl group, a dodecyl group, a dodecenyl group, atridecyl group, a tetradecyl group, a tetradecenyl group, a pentadecylgroup, a hexadecyl group, a hexadecenyl group, a heptadecyl group, anoctadecyl group, an octadecenyl group, a stearyl group, an isostearylgroup, an oleyl group, a linoleic group, a cyclopentyl group, acyclohexyl group, a methylcyclohexyl group, an ethylcyclohexyl group, apropylcyclohexyl group, a dimethylcyclohexyl group, and atrimethylcyclohexyl group; and aromatic hydrocarbon groups such as aphenyl group, a methylphenyl group, an ethylphenyl group, adimethylphenyl group, a propylphenyl group, a trimethylphenyl group, abutylphenyl group, and a naphthyl group.

The hydrocarbon group is preferably a hydrocarbon group having 1 to 18carbon atoms, more preferably a hydrocarbon group having 1 to 12 carbonatoms, still more preferably a hydrocarbon group having 1 to 4 carbonatoms, and most preferably a hydrocarbon group having 2 carbon atoms.

The oxygen-containing hydrocarbon group that contains an ether bond oran ester bond is preferably the group having 1 to 18 carbon atoms, andexamples thereof include a methoxymethyl group, an ethoxymethyl group, apropoxymethyl group, an isopropoxymethyl group, a n-butoxymethyl group,a t-butoxymethyl group, a hexyloxymethyl group, an octyloxymethyl group,a 2-ethyl-hexyloxymethyl group, a decyloxymethyl group, adodecyloxymethyl group, a 2-butyloctyloxymethyl group, atetradecyloxymethyl group, a hexadecyloxymethyl group, a2-hexyldodecyloxymethyl group, an allyloxymethyl group, a phenoxy group,a benzyloxy group, a methoxyethyl group, a methoxypropyl group, a1,1-bismethoxypropyl group, a 1,2-bismethoxypropyl group, anethoxypropyl group, a (2-methoxyethoxy)propyl group, a(1-methyl-2-methoxy)propyl group, an acetyloxymethyl group, apropanoyloxymethyl group, a butanoyloxymethyl group, a hexanoyloxymethylgroup, an octanoyloxymethyl group, a 2-ethylhexanoyloxymethyl group, adecanoyloxymethyl group, a dodecanoyloxymethyl group, a2-butyloctanoyloxymethyl group, a tetradecanoyloxymethyl group, ahexadecanoyloxymethyl group, a 2-hexyldodecanoyloxymethyl group, and abenzoyloxymethyl group.

Furthermore, b to d each represents an integer of 0 to 20.

b+c is preferably 1 to 20, more preferably 1 to 10, still morepreferably 1 to 4, and most preferably 2.

In the general formula (IV), it is preferable that all of R¹⁷ to R²⁴ area hydrogen atom. Further, in the general formula (V), it is preferablethat all of R²⁷ to R³⁰ are a hydrogen atom.

In a case where the aliphatic amine compound of the general formula (IV)is used as the amine-based ashless friction modifier (C2), the aliphaticamine compounds in which all of R¹⁶'s are all the same may be used, or amixture of the aliphatic amine compounds in which R¹⁶'s are different(for example, those in which the number of carbon atoms or the presenceor absence of a double bond is different) as for naturally derivedhydrocarbon groups such as beef tallow may be used. Similarly, in thecase where the aliphatic amine compound of the general formula (V) isused as the amine-based ashless friction modifier (C2), the aliphaticamine compounds in which R²⁵'s and R²⁶'s are all the same may be used,or a mixture of the aliphatic amine compounds in which R²⁵'s and R²⁶'sare different (for example, those in which the number of carbon atoms orthe presence or absence of a double bond is different) may be used.

Specific examples of the compounds of the general formula (IV) includeamine compounds having one 2-hydroxyalkyl group, for example, ahydroxyethyl group, such as octyl ethanolamine, decyl ethanolamine,dodecyl ethanolamine, tetradecyl ethanolamine, hexadecyl ethanolamine,stearyl ethanolamine, oleyl ethanolamine, coconut oil ethanolamine, palmoil ethanolamine, rapeseed oil ethanolamine, and beef tallowethanolamine; amine compounds having two 2-hydroxyalkyl groups, such asoctyl diethanolamine, decyl diethanolamine, dodecyl diethanolamine,tetradecyl diethanolamine, hexadecyl diethanolamine, stearyldiethanolamine, oleyl diethanolamine, coconut oil diethanolamine, palmoil diethanolamine, rapeseed oil diethanolamine, and beef tallowdiethanolamine; and amine compounds having a polyalkylene oxidestructure, such as polyoxyethylene octylamine, polyoxyethylenedecylamine, polyoxyethylene dodecylamine, polyoxyethylenetetradecylamine, polyoxyethylene hexadecylamine, polyoxyethylenestearylamine, polyoxyethylene oleylamine, polyoxyethylene beef tallowamine, polyoxyethylene coconut oil amine, polyoxyethylene palm oilamine, polyoxyethylene laurylamine, polyoxyethylene stearylamine,polyoxyethylene oleylamine, and ethylene oxide-propylene oxidestearylamine.

Specific examples of the compounds of the general formula (V) includealkylamine compounds having one 2-hydroxyalkyl group, for example,hydroxyethyl groups such as N-methyl-octyl ethanolamine, N-methyl-decylethanolamine, N-methyl-dodecyl ethanolamine, N-methyl-tetradecylethanolamine, N-methyl-hexadecyl ethanolamine, N-methyl-stearylethanolamine, N-methyl-oleyl ethanolamine, N-methyl-coconut oilethanolamine, N-methyl-palm oil ethanolamine, N-methyl-rapeseed oilethanolamine, and N-methyl-beef tallow ethanolamine; and alkylaminecompounds having a polyalkylene oxide structure, such as polyoxyethyleneN-methyl-decylamine, polyoxyethylene N-methyl-dodecylamine,polyoxyethylene N-methyl-tetradecylamine, polyoxyethyleneN-methyl-hexadecylamine, polyoxyethylene N-methyl-stearylamine, andpolyoxyethylene N-methyl-oleylamine.

The lubricating oil composition of the present embodiment may includeany one of the ester-based ashless friction modifier (C1) and theamine-based ashless friction modifier (C2) as the ashless frictionmodifier of the component (C), but it is preferable that the ester-basedashless friction modifier (C1) is used in combination with theamine-based ashless friction modifier (C2).

By using the ester-based ashless friction modifier (C1) in combinationwith the amine-based ashless friction modifier (C2), a friction-reducingeffect based on the molybdenum compound (B) can be more easilymaintained. That is, by using the ester-based ashless friction modifier(C1) in combination with the amine-based ashless friction modifier (C2),it is possible to impart a friction-reducing effect based on threecomponents of the molybdenum compound (B), the ester-based ashlessfriction modifier (C1), and the amine-based ashless friction modifier(C2), and thus, fuel consumption reducing properties can be moreimproved.

Furthermore, from the viewpoint that the effect can be easily exhibitedby using the ester-based ashless friction modifier (C1) in combinationwith the amine-based ashless friction modifier (C2), the mass ratio ofthe content of the amine-based ashless friction modifier (C2) to thecontent of the ester-based ashless friction modifier (C1) [the contentof the amine-based ashless friction modifier (C2)/the content of theester-based ashless friction modifier (C1)] is preferably less than1.00.

The ratio is more preferably 0.10 or more and 0.80 or less, and stillmore preferably 0.15 or more and 0.60 or less.

Moreover, the mass ratio of the total content of the ester-based ashlessfriction modifier (C1) and the amine-based ashless friction modifier(C2) to the content of the molybdenum compound (B) as converted intomolybdenum atoms [(the content of the ester-based ashless frictionmodifier (C1)+the content of the amine-based ashless friction modifier(C2))/the content of the molybdenum compound (B) as converted intomolybdenum atoms] is preferably 4.0 to 30.0, more preferably 5.0 to25.0, and still more preferably 6.5 to 23.0.

The ashless friction modifier (C) may contain ashless type frictionmodifiers (other ashless type friction modifiers) other than theester-based ashless friction modifier (C1) and the amine-based ashlessfriction modifier (C2), within a range not impairing the effect of thelubricating oil composition of the present embodiment. Here, the totalcontent of the ester-based ashless friction modifier (C1) and theamine-based ashless friction modifier (C2) based on the total amount ofthe ashless friction modifier (C), is preferably 80 mass % or more, morepreferably 90 mass % or more, and still more preferably 100 mass %.

<Boratad Succinimide (D)>

The lubricating oil composition of the present embodiment preferablyfurther includes a boratad succinimide (D).

By using the molybdenum compound (B), and the ester-based ashlessfriction modifier (C1) and/or the amine-based ashless friction modifier(C2), together with the boratad succinimide (D), a friction-reducingeffect based on the molybdenum compound (B) can be more easilymaintained, and as a result, the synergistic action with the molybdenumcompound (B) and the ester-based ashless friction modifier (C1) and/orthe amine-based ashless friction modifier (C2) is easily exhibited, thefriction-reducing effect is more enhanced, and the fuel consumptionreducing properties can be enhanced.

Examples of the boratad succinimide of the component (D) includeboronated products of alkenyl- or alkylsuccinic monoimide, or boronatedproducts of alkenyl- or alkylsuccinic bisimide.

Examples of the alkenyl- or alkylsuccinic monoimide include a compoundrepresented by the following general formula (VI). Further, examples ofthe alkenyl- or alkylsuccinic bisimide include a compound represented bythe following general formula (VII).

In the general formulae (VI) and (VII), R³¹, R³³, and R³⁴ are each analkenyl group or an alkyl group, and they each have a weight averagemolecular weight of preferably 500 to 3,000, and more preferably 1,000to 3,000.

If the weight average molecular weight of R³¹, R³³, and R³⁴ is 500 ormore, the solubility in a lubricating base oil can be enhanced. Further,if the weight average molecular weight is 3,000 or less, it is expectedthat the effect obtained by the present compound is appropriatelyexhibited. R³³ and R³⁴ may be the same as or different from each other.

R³², R³⁵, and R³⁶ are each an alkylene group having 2 to 5 carbon atoms,and R³⁵ and R³⁶ may be the same as or different from each other. “e”represents an integer of 1 to 10, and “f” represents 0 or an integer of1 to 10.

Here, “e” is preferably 2 to 5, and more preferably 2 to 4. If “e” is 2or more, it is expected that the effect obtained by the boratadsuccinimide is easily obtained. If “e” is 5 or less, the solubility in alubricating base oil is more enhanced.

Furthermore, “f” is preferably 1 to 6, and more preferably 2 to 6. If“f” is 1 or more, it is expected that the effect obtained by the presentcompound is appropriately exhibited. If “f” is 6 or less, the solubilityin a lubricating base oil is enhanced.

Examples of the alkenyl group include a polybutenyl group, apolyisobutenyl group, and an ethylene-propylene copolymer, and examplesof the alkyl group include hydrogenated products thereof. Suitableexamples of the alkenyl group include a polybutenyl group and apolyisobutenyl group. As the polybutenyl group, a mixture of 1-buteneand isobutene or a product obtained by polymerization of high-purityisobutene is suitably used. Further, suitable representative examples ofthe alkyl group include hydrogenated products of a polybutenyl group ora polyisobutenyl group.

The boratad succinimide (D) can be obtained by, for example, reacting apolyolefin with maleic anhydride to obtain an alkenylsuccinic anhydride(x); reacting a polyamine with a boron compound to obtain anintermediate (y); and then reacting the alkenylsuccinic anhydride (x)with the intermediate (y), followed by imidization. The monoimide or thebisimide can be produced by changing the ratio of the alkenylsuccinicanhydride or the alkylsuccinic anhydride to the polyamine.

In addition, the boratad succinimide (D) can also be produced bytreating an alkenyl- or alkylsuccinic monoimide or an alkenyl- oralkylsuccinic bisimide not containing boron with the boron compound.

As the olefin monomer that forms the polyolefin, one kind or a mixtureof two or more kinds of α-olefins having 2 to 8 carbon atoms can beused, but a mixture of isobutene and 1-butene can be suitably used.

Meanwhile, examples of the polyamine include single diamines such asethylenediamine, propylene diamine, butylendiamine, and pentylenediamine; polyalkylene polyamines such as diethylenetriamine,triethylenetetramine, tetraethylenepentamine, p entaethylenehexamine,di(methylethylene)triamine, dibutylentriamine, tributylentetramine, andpentapentylenehexamine; and piperazine derivatives such asaminoethylpiperazine.

Examples of the boron compound include boric acid, borate, and a boricacid ester.

Examples of the boric acid include orthoboric acid, metaboric acid, andparaboric acid. Further, examples of the borate include ammonium borate,such as ammonium metaborate, ammonium tetraborate, ammonium pentaborate,and ammonium octaborate. Further, examples of the boric acid esterinclude monomethyl borate, dimethyl borate, trimethyl borate, monoethylborate, diethyl borate, triethyl borate, monopropyl borate, dipropylborate, tripropyl borate, monobutyl borate, dibutyl borate, and tributylborate.

The ratio (B/N ratio) of the amount of boron atoms to the amount ofnitrogen atoms, which are contained in the boratad succinimide (D), ispreferably 0.6 or more, more preferably 0.7 or more, and still morepreferably 0.8 or more, on a mass basis, in terms of friction reduction.Further, the B/N ratio is not particularly limited, but is preferably2.0 or less, more preferably 1.5 or less, and still more preferably 1.3or less.

From the viewpoint of friction reduction, the boratad succinimide (D)preferably includes a large amount of a three-coordinate boratadsuccinimide, and specifically, includes a three-coordinate boratadsuccinimide at a molar ratio of preferably 0.50 or more, more preferably0.60 or more, and still more preferably 0.65 or more, relative to thetotal amount of three-coordinate boratad succinimide and four-coordinateboratad succinimide.

The ratio of three-coordinate boratad succinimide and thefour-coordinate boratad succinimide can be measured by, for example,¹¹B-NMR measurement as a BF₃.OEt₂ standard (0 ppm). In this ¹¹B-NMRmeasurement, the peaks of the three-coordinate boratad succinimide areshown at 5 to 25 ppm, and the peaks of the four-coordinate boratadsuccinimide are shown at −10 to 5 ppm, and thus, it is possible tocalculate the ratio by calculating the integrated value of therespective peaks.

Moreover, in the lubricating oil composition of the present embodiment,the content of the boratad succinimide (D) as converted into boron atomsis preferably 0.050 mass % or less, more preferably 0.001 to 0.050 mass%, still more preferably 0.005 to 0.040 mass %, and even still morepreferably 0.015 to 0.035 mass %, based on the total amount of thelubricating oil composition.

By allowing the content of the boratad succinimide (D) as converted intoboron atoms to fall within the range, inhibition of a friction-reducingeffect based on the molybdenum compound (B) can be suppressed, and as aresult, the synergistic action with the molybdenum compound (B), and theester-based ashless friction modifier (C1) and/or the amine-basedashless friction modifier (C2) can be more exhibited, thefriction-reducing effect can be more enhanced, and thus, the fuelconsumption reducing properties can be more improved.

Furthermore, in the lubricating oil composition of the presentembodiment, the mass ratio of the total content of the ester-basedashless friction modifier (C1) and the amine-based ashless frictionmodifier (C2) to the content of the boratad succinimide (D) as convertedinto boron atoms [the content of the boratad succinimide (D) asconverted into boron atoms/(the content of the ester-based ashlessfriction modifier (C1)+the content of the amine-based ashless frictionmodifier (C2))] is preferably 0.011 or more, more preferably 0.013 ormore and 0.100 or less, and still more preferably 0.015 or more and0.070 or less.

By allowing the ratio to fall within the range, inhibition of afriction-reducing effect based on the molybdenum compound (B) can bemore suppressed, and by the synergistic action with the molybdenumcompound (B) and the ester-based ashless friction modifier (C1), thefriction-reducing effect is more enhanced, and thus, the fuelconsumption reducing properties can be more improved.

<Poly(Meth)Acrylate (E)>

It is preferable that the lubricating oil composition of the presentembodiment further contains a poly(meth)acrylate (E) as a viscosityindex improver. By containing the poly(meth)acrylate (E), the fuelconsumption reducing properties can be more improved.

The monomer constituting the poly(meth)acrylate (E) is alkyl(meth)acrylate, and preferably alkyl (meth)acrylate with a linear alkylgroup having 1 to 18 carbon atoms or a branched alkyl group having 3 to34 carbon atoms.

Preferred examples of the monomer constituting the poly(meth)acrylate(E) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl(meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl(meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl(meth)acrylate, nonyl (meth)acrylate, decyl (meth) acrylate, dodecyl(meth) acrylate, tetra(meth)acrylate, hexa(meth)acrylate, and octadecyl(meth)acrylate, and two or more kinds of these monomers may be used as acopolymer. The alkyl group of these monomers may be linear chained orbranch chained.

Furthermore, examples of the alkyl (meth)acrylate with a branched alkylgroup having 3 to 34 carbon atoms include isopropyl (meth)acrylate,2-ethylhexyl (meth) acrylate, 3,5,5-trimethylhexyl (meth) acrylate,2-butyloctyl (meth) acrylate, 2-hexyldecyl (meth) acrylate,2-octyldodecyl (meth) acrylate, 2-decyltetradecyl (meth) acrylate,2-dodecylhexadecyl (meth) acrylate, and 2-tetradecyloctadecyl (meth)acrylate.

The weight average molecular weight of the poly(meth)acrylate (E) ispreferably 100,000 to 600,000, and more preferably 15,000 to 400,000.

Moreover, in the present embodiment, the “weight average molecularweight” refers to a molecular weight as converted into polystyrene,which is determined by a gel permeation chromatography (GPC)measurement.

The SSI of the poly(meth)acrylate (E) is preferably 50 or less, and morepreferably 1 to 30. By allowing the weight average molecular weight tofall within the above range, the SSI can be adjusted to 30 or less.

Here, the SSI means a shear stability index, and represents an abilityof resisting to decomposition of a poly(meth)acrylate. As the SSI islarger, the polymer is more unstable against shear and more easilydecomposes.

${SSI} = {\frac{{K\; v_{0}} - {K\; v_{1}}}{{K\; v_{0}} - {K\; v_{oil}}} \times 100}$

The SSI indicates a decrease in viscosity under shear derived from apolymer, and is calculated using the above calculation equation. In theequation, Kv₀ represents a value of kinematic viscosity at 100° C. of amixture obtained by adding a poly(meth)acrylate to a base oil. Kv₁ is avalue of kinematic viscosity at 100° C. measured after passing themixture obtained by the addition of poly(meth)acrylate to the base oilthrough a high-shear Bosch diesel injector for 30 cycles in accordancewith the procedures of ASTM D6278. Further, Kv_(oil) is a value ofkinematic viscosity at 100° C. of the base oil. In addition, as the baseoil, a Group II base oil having a kinematic viscosity at 100° C. of 5.35mm²/s and a viscosity index of 105 is used.

From the viewpoint of fuel consumption reducing properties, the contentof the poly(meth)acrylate (E) is preferably 0.5 to 15 mass %, morepreferably 1 to 10 mass %, and still more preferably 1 to 8 mass %,based on the total amount of the lubricating oil composition.

Here, the content of the poly(meth)acrylate means the content of onlythe resin fractions composed of poly(meth)acrylate, and is, for example,a content on a solid content basis which does not include the mass of adiluent oil and the like which are contained together with thepoly(meth)acrylate.

<Metal-Based Detergent (F)>

It is preferable that the lubricating oil composition of the presentembodiment further contains a metal-based detergent (F). By containingthe metal-based detergent (F), production of a deposit in the inside ofan engine at the time of high-temperature operation is suppressed,accumulation of a sludge is prevented to keep the inside of the engineclean, and acidic substance generated as a result of degradation and thelike of an engine oil is neutralized to prevent corrosive wear.

Examples of the metal-based detergent (F) include an alkali metal-baseddetergent or an alkaline-earth metal-based detergent. Specific examplesthereof include one or more metal-based detergents selected from alkalimetal sulfonate or alkaline-earth metal sulfonate, alkali metal phenateor alkaline-earth metal phenate, alkali metal salicylate, oralkaline-earth metal salicylate. Further, examples of the alkali metalinclude sodium and potassium, examples of the alkaline-earth metalinclude magnesium and calcium, and among these, sodium which is analkali metal, and magnesium and calcium which are alkaline-earth metalsare preferable, and calcium is more preferable.

The metal-based detergent (F) may be neutral, basic, or overbasic, butis preferably basic or overbasic. Further, the total base number of themetal-based detergent (F) is preferably 10 to 500 mgKOH/g, and morepreferably 150 to 450 mgKOH/g. Further, the total base number is one asmeasured in accordance with a perchloric acid method of JIS K2501.

From the viewpoint of exhibiting an effect based on the above-mentionedmetal-based detergent (F), the content of the metal-based detergent (F)as converted into a metal amount in the lubricating oil composition ofthe present embodiment is preferably 0.05 to 0.50 mass %, and morepreferably 0.10 to 0.30 mass %, based on the total amount of thelubricating oil composition.

<Zinc Dithiophosphate (G)>

It is preferable that the lubricating oil composition of the presentembodiment further contains zinc dithiophosphate (G). By containing zincdithiophosphate of the component (G), the friction-reducing effect canbe more enhanced.

Examples of the zinc dithiophosphate (G) include those represented bythe following general formula (VIII):

in the formula, R³⁷ to R⁴⁰ each independently represents any oneselected from a linear, branched, or cyclic alkyl group having 6 to 20carbon atoms, and a linear, branched, or cyclic alkenyl group having 6to 20 carbon atoms.

By allowing the number of carbon atoms of R³⁷ to R⁴⁰ in the generalformula (VIII) to be 6 to 20, a balance between the solubility in alubricating base oil and the friction reduction can be enhanced.

The number of carbon atoms of the alkyl group or the alkenyl group ofR³⁷ to R⁴⁰ in the general formula (VIII) is preferably 8 to 18, and morepreferably 10 to 14. Further, R³⁷ to R⁴⁰ in the general formula (VIII)are each preferably an alkyl group.

Examples of the alkyl group in R³⁷ to R⁴⁰ include a methyl group, anethyl group, a propyl group, a butyl group, a pentyl group, a hexylgroup, a heptyl group, an octyl group, a nonyl group, a decyl group, anundecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, apentadecyl group, a hexadecyl group, a heptadecyl group, an octadecylgroup, a nonadecyl group, an eicosyl group, a heneicosyl group, adocosyl group, a tricosyl group, and a tetracosyl group, and these maybe linear, branched, or cyclic. Further, examples of the alkenyl groupinclude a vinyl group, a propenyl group, a butenyl group, a pentenylgroup, a hexenyl group, a heptenyl group, an octenyl group, a nonenylgroup, a decenyl group, an undecenyl group, a dodecenyl group, atridecenyl group, a tetradecenyl group, a pentadecenyl group, ahexadecenyl group, a heptadecenyl group, an octadecenyl group, anonadecenyl group, an eicosenyl group, a heneicosenyl group, a docosenylgroup, a tricosenyl group, and a tetracosenyl group. These may belinear, branched, or cyclic, and the position of the double bond isarbitrary.

In the general formula (VIII), R³⁷ to R⁴⁰ may be the same as ordifferent from each other, and from the viewpoint of easiness in termsof production, they are preferably the same as each other.

Among these, dodecyl groups such as a lauryl group, octadecyl groupssuch as a tetradecyl group, a hexadecyl group, and a stearyl group, andoctadecenyl groups such as an eicosyl group and an oleyl group arepreferable, and a lauryl group is the most preferable.

From the viewpoint of a balance between friction reduction and abrasionresistance, the content of zinc dithiophosphate (G) is preferably 0.01to 3.00 mass %, and more preferably 0.10 to 1.50 mass %, based on thetotal amount of the lubricating oil composition.

Furthermore, the content of zinc dithiophosphate (G) as converted intophosphorus atoms is preferably 100 to 2,000 ppm, more preferably 300 to1,500 ppm, still more preferably 500 to 1,000 ppm, and even still morepreferably 600 to 840 ppm, based on the total amount of the lubricatingoil composition.

<Arbitrary Additive Components>

The lubricating oil composition of the present embodiment may containarbitrary additive components such as succinimide not containing boron,an antioxidant, a rust inhibitor, a metal deactivator, a pour-pointdepressant, and an antifoaming agent as arbitrary components.

The content of these arbitrary additive components is approximately 0.01to 5.00 mass % based on the total amount of the lubricating oilcomposition.

<Physical Properties of Lubricating Oil Composition>

From the viewpoint of friction reduction over a wide temperature rangefrom a low temperature to a high temperature, it is preferable that thelubricating oil composition of the present embodiment has a kinematicviscosity at 40° C., a kinematic viscosity at 100° C., and an HTHSviscosity at 150° C., each of which falls within the following range.

The kinematic viscosity at 40° C. is preferably 20 to 40 mm²/s, and morepreferably 20 to 35 mm²/s.

The kinematic viscosity at 100° C. is preferably 3.0 to 12.5 mm²/s, andmore preferably 4.0 to 9.3 mm²/s.

The HTHS viscosity at 150° C. is preferably 1.4 to 2.9 mPa·s, and morepreferably 1.7 to 2.9 mPa·s.

Furthermore, the kinematic viscosity was measured in conformity with JISK2283. The HTHS viscosity was measured using a TBS viscometer (taperedbearing simulator viscometer) in accordance with ASTM D4683 under theconditions at an oil temperature of 100° C., a shear rate of 10⁶/s, arotational speed (motor) of 3,000 rpm, and a clearance (clearancebetween a rotor and a stator) of 3 μm.

<Application of Lubricating Oil Composition>

The lubricating oil composition of the present embodiment is notparticularly limited with respect to its application, but it can besuitably used for a variety of internal combustion engines of afour-wheel automobile, a two-wheel automobile, or the like. Further,among the internal combustion engines, the lubricating oil compositionof the present embodiment can be particularly suitably used for agasoline engine.

[Method for Reducing Friction of Internal Combustion Engine]

The method for reducing friction of an internal combustion engine of thepresent embodiment includes adding the above-mentioned lubricating oilcomposition of the present embodiment to an internal combustion engine.

According to the method for reducing friction of an internal combustionengine of the present embodiment, inhibition of a friction-reducingeffect based on the molybdenum compound (B) is suppressed; and by thesynergistic action with the molybdenum compound (B), and the ester-basedashless friction modifier (C1) and/or the amine-based ashless frictionmodifier (C2), the friction-reducing effect is enhanced, and thus, thefuel consumption reducing properties can be enhanced. In a case wherethe internal combustion engine is a gasoline engine, the effect can beparticularly enhanced.

Examples

Next, the present invention will be described in more detail withreference to Examples, but it should be construed that the presentinvention is by no means limited by these Examples.

1. Preparation of Lubricating Oil Compositions of Examples andComparative Examples

Lubricating oil compositions of Examples and Comparative Examples wereprepared in the compositions shown in Tables 1 to 3. Further, for thepreparation of the lubricating oil compositions, the following materialswere used.

<Lubricating Base Oil (A)>

Mineral oil having a kinematic viscosity at 100° C.: 4.07 mm²/s,viscosity index: 131, % C_(A): −0.4, % C_(N): 12.8, and % C_(P): 87.6

<Molybdenum Compound (B)>

Binuclear organic molybdenum compound of the general formula (I) (MoDTChaving an Mo content of 10 mass %)

<Ester-Based Ashless Friction Modifier (C1)>

Glycerin monooleate (number of hydroxyl groups in one molecule: 2)

<Amine-Based Ashless Friction Modifier (C2)>

Alkyldiethanolamine (the number of carbon atoms of an alkyl group beinga mixture of 12 to 20)

<Boratad Succinimide (D)>

Boratad polybutenylsuccinic bisimide (boron content: 1.3 mass %,nitrogen content: 1.2 mass %, amount of boron atoms/amount of nitrogenatoms: 1.1)

<Poly(Meth)Acrylate (E)>

Polymethacrylate (weight average molecular weight of 440,000, content ofthe resin fraction of 17%, SSI of 30)

<Metal-Based Detergent (F)>

Calcium-based detergent (calcium content: 12.1 mass %, overbasic, totalbase number: 350 mgKOH/g)

<Zinc Dithiophosphate (G)>

ZnDTP (phosphorus content: 7.0 mass %, zinc content: 8.0 mass %, sulfurcontent: 14.0 mass %)

<Other Components>

Polybutenylsuccinic bisimide which is not a boratad material, a hinderedphenol-based antioxidant, a diphenylamine-based antioxidant, apour-point depressant, a metal deactivator, and an antifoaming agent

2. Measurement and Evaluation

The lubricating oil compositions of Examples and Comparative Exampleswhich had been prepared in the compositions shown in Tables 1 to 3 weresubjected to the following evaluations. The results are shown in Tables1 to 3.

2-1. HTHS Viscosity

In accordance with the disclosure of the present specification, the HTHSviscosity at 150° C. of the lubricating oil composition was measured.

2-2. Friction Coefficient (HFRR Test)

Using an HFRR tester (manufactured by PCS Instruments), the frictioncoefficient of the lubricating oil composition was measured under thefollowing conditions. A lower friction coefficient may indicate that thefriction-reducing effect is superior and the fuel consumption reducingproperties are better.

-   -   Test piece: (A) Ball=HFRR standard test piece (AISI 52100        material), (B) Disc=HFRR standard test piece (AISI 52100        material)    -   Amplitude: 1.0 mm    -   Frequency: 50 Hz    -   Load: 5 g    -   Temperature: 80° C.

In Tables 1 to 3, [mass % of Mo] represents the content of themolybdenum compound (B) as converted into molybdenum atoms based on thetotal amount of the lubricating oil composition; [mass % of B]represents the content of the boratad succinimide (D) as converted intoboron atoms based on the total amount of the lubricating oilcomposition; and [mass % of Metal] represents the content of themetal-based detergent (F) as converted into metal atoms (calcium atoms)based on the total amount of the lubricating oil composition.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 1 Example 2Composition Lubricating base oil (A) mass % Balance Balance BalanceBalance Molybdenum compound (B) mass % 0.7 0.7 0.7 0.7 Ester-basedfriction modifier (C1) mass % 0.5 — — — Amine-based friction modifier(C2) mass % — 0.5 — 2.0 Boratad succinimide (D) mass % 2.3 2.3 2.3 2.3Poly(meth)acrylate (E) mass % 10.3 10.3 10.3 10.3 Metal-based detergent(F) mass % 1.65 1.65 1.65 1.65 Zinc dithiophosphate (G) mass % 1.14 1.141.14 1.14 Other components mass % 6.16 6.16 6.16 6.16 Properties ofContent of molybdenum mass % 0.070 0.070 0.070 0.070 lubricating oilderived from (B) of Mo composition Content of boron mass % 0.030 0.0300.030 0.030 derived from (D) of B Content of metal derived mass % 0.2000.200 0.200 0.200 from (F) of metal HTHS viscosity at 150° C. mPa · s2.6 2.6 2.6 2.6 Evaluation Friction coefficient — 0.057 0.057 0.0650.109

As is clear from the results of Table 1, it can be confirmed that thelubricating oil compositions of Examples 1 and 2, each including themolybdenum compound (B), and a specific amount of the ester-basedashless friction modifier (C1) and/or the amine-based ashless frictionmodifier (C2), exhibit a better friction-reducing effect, as comparedwith the lubricating oil composition of Comparative Example 1, notincluding the ester-based ashless friction modifier (C1) and/or theamine-based ashless friction modifier (C2).

It can also be confirmed that the lubricating oil composition ofComparative Example 2, including more than an appropriate amount of theester-based ashless friction modifier (C1) and/or the amine-basedashless friction modifier (C2) does not exhibit a good friction-reducingeffect. The reason for this may be thought to be that thefriction-reducing effect of the molybdenum compound (B) is inhibited bya large amount of the ester-based ashless friction modifier (C1) and/orthe amine-based ashless friction modifier (C2).

TABLE 2 Example Comparative 3 4 5 6 7 8 9 Example 3 CompositionLubricating base oil (A) mass % Balance Balance Balance Balance BalanceBalance Balance Balance Molybdenum compound (B) mass % 0.7 0.7 0.7 0.70.3 0.7 0.7 0.7 Ester-based friction mass % 1.0 — 1.0 0.5 0.5 1.0 0.52.0 modifier (C1) [X] Amine-based friction mass % — 0.5 0.1 0.1 0.1 0.50.5 0.5 modifier (C2) [Y] Boratad succinimide (D) mass % 2.3 2.3 2.3 2.32.3 2.3 2.3 2.3 Poly(meth)acrylate (E) mass % 10.3 10.3 10.3 10.3 10.310.3 10.3 10.3 Metal-based detergent (F) mass % 1.65 1.65 1.65 1.65 1.651.65 1.65 1.65 Zinc dithiophosphate (G) mass % 1.14 1.14 1.14 1.14 1.141.14 1.14 1.14 Other components mass % 6.16 6.16 6.16 6.16 6.16 6.166.16 6.16 Properties of Content of molybdenum mass % 0.070 0.070 0.0700.070 0.030 0.070 0.070 0.070 lubricating derived from (B) of Mo oilContent [Z] of boron mass % 0.030 0.030 0.030 0.030 0.030 0.030 0.0300.030 composition derived from (C) of B Content of metal derived mass %0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 from (F) of Metal[Y]/[X] — — — 0.10 0.20 0.20 0.50 1.00 0.25 [Z]/[X + Y] — 0.026 0.0520.024 0.043 0.043 0.017 0.026 0.010 HTHS viscosity at 150° C. mPa · s2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 Evaluation Friction coefficient — 0.0540.057 0.054 0.051 0.051 0.043 0.058 0.065

From the results shown in Table 2, it can be confirmed that by using theester-based ashless friction modifier (C1) in combination with theamine-based ashless friction modifier (C2), and allowing the mass ratio([Y]/[X]) of the content [Y] of the amine-based ashless frictionmodifier (C2) to the content [X] of the ester-based ashless frictionmodifier (C1) to be less than 1.0, the friction-reducing effect can bemore enhanced. In particular, it can be confirmed that the lubricatingoil compositions of Examples 6 to 8, each having [Y]/[X] of more than0.10 and less than 1.00, exhibit a highly excellent friction-reducingeffect.

In addition, in Comparative Example 3, the ester-based ashless frictionmodifier (C1) is used in combination with the amine-based ashlessfriction modifier (C2), but the friction coefficient increases. Thereason for this may be thought to be that in Comparative Example 3, thetotal amount of the ester-based ashless friction modifier (C1) and theamine-based ashless friction modifier (C2) is more than 1.8 mass % basedon the total amount of the lubricating oil composition, so that thefriction-reducing effect of the molybdenum compound (B) is inhibited.

TABLE 3 Example 6 Example 10 Composition Lubricating base oil (A) mass %Balance Balance Molybdenum compound (B) mass % 0.7 0.7 Ester-basedfriction modifier (C1) mass % 0.5 0.5 Amine-based friction modifier (C2)mass % 0.1 0.1 Boratad succinimide (D) mass % 2.3 — Poly(meth)acrylate(E) mass % 10.3 12.0 Metal-based detergent (F) mass % 1.65 1.65 Zincdithiophosphate (G) mass % 1.14 1.14 Other components mass % 6.16 6.16Properties Content of molybdenum derived mass % of 0.070 0.070 from (B)Mo Content of boron derived from (C) mass % of B 0.030 — Content ofmetal derived from (F) mass % of 0.200 0.200 metal HTHS viscosity at150° C. mPa · s 2.6 2.6 Evaluation Friction coefficient — 0.051 0.059

From the results shown in Table 3, it can be confirmed that thelubricating oil composition of Example 6, including the molybdenumcompound (B), the ester-based ashless friction modifier (C1) and/or theamine-based ashless friction modifier (C2), and the boratad succinimide(D) exhibits a better friction-reducing effect, as compared with thelubricating oil composition of Example 10, including the molybdenumcompound (B), the ester-based ashless friction modifier (C1) and/or theamine-based ashless friction modifier (C2), but not including theboratad succinimide (D). The reason for this may be thought to be thatin the lubricating oil composition of Example 6, by using the molybdenumcompound (B), and the ester-based ashless friction modifier (C1) and/orthe amine-based ashless friction modifier (C2), together with theboratad succinimide (D), a friction-reducing effect based on themolybdenum compound (B) is more easily retained, and by the synergisticaction with the molybdenum compound (B), and the ester-based ashlessfriction modifier (C1) and/or the amine-based ashless friction modifier(C2), the friction-reducing effect is more enhanced.

INDUSTRIAL APPLICABILITY

The lubricating oil composition of the present embodiment exhibits agood friction-reducing effect, and thus, the fuel consumption reducingproperties can be enhanced. For this reason, the lubricating oilcomposition of the present embodiment can be suitably used for a varietyof internal combustion engines of a four-wheel automobile, a two-wheelautomobile, or the like. Further, among the internal combustion engines,the lubricating oil composition of the present embodiment can beparticularly suitably used for a gasoline engine.

1. A lubricating oil composition, comprising: a lubricating base oil(A); a molybdenum compound (B); and an ashless friction modifier (C),wherein the lubricating oil composition includes: a binuclear organicmolybdenum compound represented by the following general formula (I) asthe molybdenum compound (B):

with a content of the binuclear organic molybdenum compound as convertedinto molybdenum atoms being 0.030 mass % or more and 0.140 mass % orless based on a total amount of the lubricating oil composition; and anester-based ashless friction modifier (C1), an amine-based ashlessfriction modifier (C2), or both, as the ashless friction modifier (C),with a total content of the ester-based ashless friction modifier (C1)and the amine-based ashless friction modifier (C2) being more than 0.1mass % and 1.8 mass % or less based on the total amount of thelubricating oil composition, wherein: R¹ to R⁴ each represents ahydrocarbon group having 4 to 22 carbon atoms, and R¹ to R⁴ may be thesame as or different from each other; and X¹ to X⁴ each represents asulfur atom or an oxygen atom.
 2. The lubricating oil compositionaccording to claim 1, comprising, as the ester-based ashless frictionmodifier (C1), an ester compound having one or more hydroxyl groups in amolecule thereof.
 3. The lubricating oil composition according to claim2, wherein the ester compound having one or more hydroxyl groups in amolecule thereof is glycerin monooleate.
 4. The lubricating oilcomposition according to claim 1, comprising the ester-based ashlessfriction modifier (C1) and the amine-based ashless friction modifier(C2), as the ashless friction modifier (C).
 5. The lubricating oilcomposition according to claim 4, wherein a mass ratio between a contentof the amine-based ashless friction modifier (C2) and a content of theester-based ashless friction modifier (C1) [the content of theamine-based ashless friction modifier (C2)/the content of theester-based ashless friction modifier (C1)] is less than 1.00.
 6. Thelubricating oil composition according to claim 1, further comprising aboratad succinimide (D).
 7. The lubricating oil composition according toclaim 6, wherein a content of the boratad succinimide (D) as convertedinto boron atoms is 0.050 mass % or less based on the total amount ofthe lubricating oil composition.
 8. The lubricating oil compositionaccording to claim 6, comprising the ester-based ashless frictionmodifier (C1) and the amine-based ashless friction modifier (C2), as theashless friction modifier (C), wherein a mass ratio of a total contentof the ester-based ashless friction modifier (C1) and the amine-basedashless friction modifier (C2) to a content of the boratad succinimide(D) as converted into boron atoms [the content of the boratadsuccinimide (D) as converted into boron atoms/(the content of theester-based ashless friction modifier (C1)+the content of theamine-based ashless friction modifier (C2))] is 0.011 or more.
 9. Thelubricating oil composition according to claim 1, further comprising apoly(meth)acrylate (E).
 10. The lubricating oil composition according toclaim 1, further comprising a metal-based detergent (F).
 11. Thelubricating oil composition according to claim 1, further comprisingzinc dithiophosphate (G).
 12. The lubricating oil composition accordingto claim 1, wherein the lubricating base oil (A) is one or more selectedfrom mineral oils or synthetic oils classified into Group 3 and Group 4in the base oil classification of the American Petroleum Institute. 13.The lubricating oil composition according to claim 1, which is adaptedto function as a lubricating oil for an internal combustion engine. 14.A method for reducing friction of an internal combustion engine, themethod comprising adding the lubricating oil composition of claim 1 toan internal combustion engine.